864 lines
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864 lines
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
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<html>
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<head>
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<title>The Answer Guy Issue 16</title>
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</head>
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<BODY BGCOLOR="#EEE1CC" TEXT="#000000" LINK="#0000FF" VLINK="#0020F0"
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ALINK="#FF0000" >
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<!--endcut ========================================================= -->
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<H4>"Linux Gazette...<I>making Linux just a little more fun!</I>"
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</H4>
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<P> <hr> <P>
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<!-- =============================================================== -->
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<center>
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<H1><A NAME="answer">
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<img src="../gx/ans.gif" alt="" border=0 align=middle>
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The Answer Guy
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<img src="../gx/ans.gif" alt="" border=0 align=middle>
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</A></H1> <BR>
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<H4>By James T. Dennis,
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<a href="mailto:jimd@starshine.org">jimd@starshine.org</a><BR>
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Starshine Technical Services, <A HREF="http://www.starshine.org/">
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http://www.starshine.org/</A> </H4>
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</center>
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<p><hr><p>
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<H3>Contents:</H3>
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<ul>
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<li><a HREF="./answer.html#address">SATAN URL Correction</a>
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<li><a HREF="./answer.html#edi">EDI on Linux</a>
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<li><a HREF="./answer.html#zmod">zmodem</a>
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<li><a HREF="./answer.html#run">Running the Internet with Linux</a>
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<li><a HREF="./answer.html#spawn">Respawning Too Fast</a>
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<li><a HREF="./answer.html#map">Problems with Keyboard Mapping</a>
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<li><a HREF="./answer.html#modsp">Modem Speed</a>
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<li><a HREF="./answer.html#duplic">Duplicating a Linux Installed Hard Drive</a>
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<li><a HREF="./answer.html#fire">Using Linux Box as a Firewall</a>
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</ul>
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<p><hr><p>
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<a name="address"></a>
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<h3><img align=bottom alt=" " src="../gx/ques.gif">
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SATAN URL Correction
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</h3>
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<P> <B>
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From: Richard White, <a href="mailto:whiter@digex.net">whiter@digex.net</a><br>
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In the Linux Journal #14, you made reference to
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ftp.cs.perdue.edu...(grin) Doesn't exist. I think that it was supposed
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to be ftp.cs.purdue.edu.
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</B><p><b>
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-- Richard D. White, Business Connectivity Technical Support
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</B> <P>
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<img align=bottom alt=" " src="../gx/ans2.gif">
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Yes! That was, of course, a typo.
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But other than that -- did you find the info useful?
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<P> <img align=bottom alt=" " src="../gx/ques.gif">
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<B>
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Yes. Very. I've just downloaded SATAN and a few of the other security
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tools. I work in customer service for leased lines and I occasionally
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assist customers in configuring their firewalls. Learning what holes there
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are and how to plug them is very worthwhile knowledge.
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</B> <P>
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<img align=bottom alt=" " src="../gx/ans2.gif">
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Have you tried cops (Dan Farmer's earlier host based
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auditing package) or Tiger (Texas A&M University)?
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<p>
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Have you gotten tripwire running? I (and most of the
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rest of the Linux community that's tried it) had a
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little trouble with Tripwire. I had fussed it into
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submission a number of months ago -- forgotten about
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it. Then recently I had to fetch and build a new
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copy.
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<p>
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I encountered the same problems building it -- and the
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same problems with the README.linux I found myself
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muttering that someone -- anyone -- ought to prepare
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a proper set of patches that allow the Linux user to
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just compile the thing with minimal effort.
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<p>
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Now I'm not a programmer (although I do "play one
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on the 'net") so I really didn't feel qualified to
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do this. However I never have been able to inspire
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or manage much of a volunteer effort in others so
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I did it myself.
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<p>
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Creating a set of patches involved teaching myself
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how to use CVS (version control system). I'm thinking
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of writing up an article on using CVS to track local
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changes in downloaded source trees and cutting diffs
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so you can share the work you do with others on the
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net.
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<p>
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Naturally I'd use tripwire as one example --
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probably pgp as another. I'm also planning on
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importing my kernel sources into CVS.
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<p>
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If your interested you could get my patch and let
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me know if it works. It's about 150 lines of text
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that seems to work for me using Larry Wall's standard
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'patch' program.
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<p>
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-- Jim
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<p><hr><p>
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<!--================================================================-->
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<a name="edi"></a>
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<h3><img align=bottom alt=" " src="../gx/ques.gif">
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EDI On Linux
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</h3>
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<P> <B>
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From: Adam Morrisom, <A HREF="mailto:adam@morrison.iserv.net">
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adam@morrison.iserv.net</A> <br>
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I have just got management to permit me to install our first Linux box, right
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next to our not-so-mighty RS/6000. So far it has operated flawlessly (which
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is exactly what I expected). And suddenly Linux is a possible solution for
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jst about every problem we have (they loved the price tag). Now I have to
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implement EDI, and I was wondering if any software is available for Linux, I
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haven't been able to find anything, on the software map, sunsite or any where
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else. Any pointers or people to contact would be greatly appreciated.
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</B> <P> <B>
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Adam,
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</B> <P>
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<img align=bottom alt=" " src="../gx/ans2.gif">
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You certainly put in an good entry in Jim's
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"Stump the techie" contest.
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<p>
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I've heard of EDI (electronic data interchange) and
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vaguely recalled that it is a data format specification
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for electronic commerce (mostly in the mainframe world
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where X.25 predominates over TCP/IP).
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<p>
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However I haven't heard of any projects or products
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being available specifically for Linux.
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<p>
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Here's a few web pages that I did dig up that might
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help:
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<ul>
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<li><a href="http://www.spedi.com/products/unix.html">
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St. Paul Software Products - UNIX</a>
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<li><a href="http://www.marin.cc.ca.us/~shadow/bookmark.html">
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Shad's Bookmark file</a>
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<li><a href="http://www.premenos.com/">
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Premenos Technology Corporation</a>
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<li><a href="http://www.teren.com/edi.html">
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More About Electronic Data Interchange (EDI)</a>
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<li>
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RFC Archives -- RFC1767 (link dead 2-Apr-2001: article removed)
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<li><a href="ftp://ds.internic.net/rfc/rfc1767.txt">
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TSI International</a>
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<li><a href="http://www.tsisoft.com/pages/hotlinks.htm">
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1994 EDI-L (Electronic Data Interchange Issues)</a>
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<li><a href="http://www.ima.com/mlarchive/lists/edi-l.1994/0241.html">
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Mailing List Archive: Re: PC based EDI</a>
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<li><a href="http://www.uniforum.org/news/html/publications/ufm/\1995-Indes.html
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#anchor5495158">
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Uniforum: 1995 Index</a>
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</ul>
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<P>
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I hope these help. Basically it looks like there are
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not "shrinkwrap" or "off-the-shelf" EDI packages for any
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platform. Good luck.
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<p>
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One approach you may take is to contact the publishers
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or authors of your existing EDI applications and see if
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they can do the port for you.
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<p>
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-- Jim
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<p><hr><p>
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<!--================================================================-->
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<a name="zmod"></a>
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<h3><img align=bottom alt=" " src="../gx/ques.gif">
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zmodem
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</h3>
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<P> <B>
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Help answer guy! I cannot download from the net! Here's the story:
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- I run linux v2.0.0. I am using minicom v1.71. I have NOT touched my
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file transfer protocols since I installed, so they would be the
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default configs.
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</B> <P>
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<img align=bottom alt=" "src=" ../gx/ans2.gif">
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I hate debugging serial line problems.
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<p> Here's the basic litany for solving modem problems:
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<p> What happens at lower speeds? What IRQ is this serial
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line using? What sort of UART is installed?
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What are the flow control settings? Does the cable
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have conductors for all of the flow control signals?
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How is the modem configured (hardware and init strings)?
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<p> minicom 1.71 is pretty old. I have 1.75 here -- and
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there may be even newer versions up on sunsite.
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<p> Incidentally -- you should probably upgrade to
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Linux kernel version 2.0.29 or so.
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<p> Your problem may not be related to either of these
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factors -- but it won't hurt to upgrade.
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<p> The first thing I'd check is Minicom's configuration
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for init strings and flow control. Try an init string
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of:
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<PRE>
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AT&C1&D2
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</PRE>
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<p> ... (which I remember from years of supporting
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PCAnywhere as well as seeing it in my current
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configuration). These set the modem's behavior
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for the DCD (device carrier detect) and flow control.
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I don't remember which is which and what the other
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numbers do -- look them up in your modem's manual if
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you're curious).
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<p> Then make sure that minicom's "Serial port setup"
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specifies "Hardware Flow Control" is "on."
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<p> When having problems with serial lines and modems I
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find it handy to get the digital equivalent of a
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"second opinion." -- Do you run any other comm
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software on this system (pppd, uucp/cu, mgetty --
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dial-in, seyon)? Do those work reliably when transferring
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data (putting the line under load)?
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<p> I'd suggest getting a copy of C-Kermit from Columbia
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University <a href="mailto:kermit.columbia.edu">kermit.columbia.edu
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</a>. No offense to
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Miguel van Smoorenburg but minicom was having problems
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on my system, too. C-Kermit is doesn't have any of the
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full screen, ncurses "feel" to it but does a good solid
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job of talking to the modem. It's scripting capabilities
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are also far more advanced than minicom's 'runscript' --
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and has features that would be to force 'minicom' to
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do through an 'expect' script (for example).
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<p> Do you have another account on another system (BBS or
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ISP)? Do your file transfers work O.K. to or from
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there? The problem may be with your ISP rather than
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at your end.
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<p> What if you try a different protocol -- such as
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kermit? Kermit is often characterized as "slow"
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compared to zmodem -- but this is largely because
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it's default is tuned for the very noisy, unreliable
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connections that were common when it was created
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(almost 20 years ago).
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<p> After checking with another comm. program I'd look a
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little lower. Using the commands:
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<PRE>
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stty -a < /dev/modem
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</PRE>
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<p> ... and
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<PRE>
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setserial -a /dev/modem
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</PRE>
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<p> (both of these assuming you have a "modem" link to
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the appropriate <code>/dev/ttyS*</code> entry on your system).
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<p> Make sure that your stty reports crtscts (for the
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flow control). Then make sure that the cable between
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your computer and your modem has all those pins
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connected.
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<p> Double check that you don't have an IRQ conflict. These
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are insidious in that they may not show up until the
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port is under load.
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<p> In addition check to see that you have a high speed
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UART (16550AFN) on that port.
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<p> Next I'd check the modem's configuration. You can
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see some of that with AT&V (which on many Hayes
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modems dumps the configuration date and S-register
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values to your terminal). Look at the Init strings
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that you are using in Minicom and look in the
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modem manual for recommended init strings for similar
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software.
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<p> After checking all of that I'd shutdown and boot
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up in DOS (if you don't have a copy of DOS you can
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consider downloading a copy of Caldera's OpenDOS.
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I'm not sure what the licensing terms will be -- but
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I did read that we're all invited to play with it for
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90 days). Along with a copy of DOS you also need
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a Telix, Qmodem, Procomm, or other comm. package.
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There are many of these in shareware -- Telix is my
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personal favorite.
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<p> (Note: I am not advocating use of these packages
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without respect to their licenses. If you choose to
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continue to use Telix or OpenDOS -- even for the
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occasional troubleshooting session; please read and
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abide by their licensing and registration. Yes,
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I have fully legal copies of Telix (DOS and Windows)).
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<p> In any event I like to check from plain old DOS
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since the old real mode program loader is so
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minimal. You could try building a Linux kernel
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with no support for TCP/IP and stripping out all
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of the device drivers except the serial and console
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support and booting that in single user mode ... and
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that still isn't close.
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<p> The idea is to see if any of your other devices or
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hardware features are conflicting.
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<P> <B>
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<img align=bottom alt=" " src=" ../gx/ques.gif">
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i am a best internet shell account, i believe iris but i don't
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know the version.
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</B> <P>
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<img align=bottom alt=" " src=" ../gx/ans2.gif">
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I'm guessing that you mean that your account is at
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best.com and that they are running Irix (SGI).
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(Which is interesting -- since I would have guessed
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Sun/Solaris for them -- but what do I know).
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<p> Note: Irix and Solaris are not known for sterling
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serial line support. They are currently geared for
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ethernet TCP/IP support -- on the assumption that
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most sites will use terminal servers (small dedicate
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devices that convert serial connections to telnet
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sessions). Consequently I've heard that the copies
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of rz/sz that ship with these should routinely be
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replace with newer sources from the 'net.
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<P> <B>
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<img align=bottom alt=" " src=" ../gx/ques.gif">
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i have a usrobotics sportster 28.8 modem
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</B> <P>
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<img align=bottom alt=" " src=" ../gx/ans2.gif">
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Internal or external?
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<p> Personally I don't like the Sportster series.
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Their Courier's are nice (but spendy). I currently
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use a Practical Peripherals -- but my next modem will
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probably be a Zyxel.
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<P> <B>
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<img align=bottom alt=" " src=" ../gx/ques.gif">
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I type<code>sz <filename></code>
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things go along fine until about 40k than i will get a couple of different
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error messages:
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<PRE>
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BAD CRC:0
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</PRE>
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sometimes followed by another attempt at downloading
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(usually only a bit or two) than the same error OR
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<PRE>
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GARBAGE COUNT EXCEEDED:0
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</PRE>
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followed by a time-out.
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<p>AARRGH! what the heck is going on? u can email me privately if you would
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prefer, as this is probably a totally common problem and i am just not
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looking in the right place!
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</B> <P>
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</H3> <img align=bottom alt=" " src=" ../gx/ans2.gif">
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<p> My guess would that you don't have a high speed UART.
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Or that your flow control isn't properly set.
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<p> The reason I guess this is that 40K is a reasonable
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amound of data for the modem to get and buffer while
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you system does a context switch. The buffer overruns
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(in a 16450 -- older, low-speed UART) could easily be
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fatal to the transfer in the first context switch.
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<p> With the 16550 UART -- the UART has a 16 byte FIFO
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buffer. That's enough for the UART to change
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the state on the handshaking lines (lowering the
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CTR -- clear to receive -- line) and enough still
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store the incoming data while the other system
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responds (stops sending).
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<p> At 28.8Kbps coming into a 16450's (one byte!) buffer
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the sender will have tossed a lot of bits out before
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getting the message (that your system is dropping
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them all on the floor).
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<p> I am copying this to the Linux Gazette *because* it
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is a common problem. Most of us in the real world
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use modem -- we don't have T1's or ISDN/ethernet
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bridges (actually I do have a Tracell WebRamp but
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I'm not using it yet). So we are still stuck fighting
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with these problems.
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<p> I'm hoping that USB (IEEE 1394 "Firewire") actually
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takes off in the next year. It's been hanging in the
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wings, timidly for about two years now and it's LONG
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overdue.
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<p> Has anyone out there run a USB board under Linux?
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<p> For those who are lost about "Firewire" refer to:
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<ul>
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<li><a href="http://www.usar.com/indact/standard/firewf.htm">
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USAR Systems -- Fireware Info</a>
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<li><a href="http://www.adaptec.com/firewire/1394main.html">
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The IEEE-1394 High Performance Serial Bus -- Adaptec's FAQ</a>
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<li><a href="http://www.1394ta.org">
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IEEE 1394 Trade Assoc. -- Firewire, USB, serial bus</a>
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</ul>
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<p> If you have any Linux news on this topic -- mail it to
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<a href="mailto:linux-questions-only@ssc.com">linux-questions-only@ssc.com</a>.
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<p>
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--Jim
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<p><hr><p>
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<!--================================================================-->
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<a name="run"></a>
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<h3><img align=bottom alt=" " src="../gx/ques.gif">
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Running the Internet with Linux
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</h3>
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<P> <B>
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From:Ricardo Romero <a
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href="mailto:rromero@netfriendly.com"> rromero@netfriendly.com</a>
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<p>Hi, my name is Ricardo Ribeiro Romero and i live in Brazil, i try to run
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INTERNET from linux but this not run, you may help-me?
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<P>Tks, <BR>
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Romero, Ricardo
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</B> <P>
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</H3> <img align=bottom alt=" " src=" ../gx/ans2.gif">
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At the risk of seeming unfriendly, Romero, I'd have to
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suggest that you might want to look for a local consultant
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or computer specialist to help you.
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<p> Questions to a publication -- particularly a free publication
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which is entirely supported by the volunteer efforts of the
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writers and the generous sponsorship of SSC have to be
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fairly specific and of reasonably broad interest.
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<p> Any reasonable distribution of Linux includes all of the
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utilities you need to connect to the Internet as a client
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and all of the utilities that most people would ever want
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to be a service provider.
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<p> It is not clear from your message whether you are trying
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to set your system up as a server/provider or as a client
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or both.
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<p> There are several good books that go into broad coverage
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of Networking with Linux (which is largely the same as
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networking under other forms of Unix). My personal favorite
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would be the Linux Documentation Project's Network Administrator's
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Guide (LDP NAG for short). This is available electronically
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(as text, postscript, TeX, or HTML) and is probably on any
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set of CD's that you'd buy. You can also purchase a professionally
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bound and printed copy from O'Reilly & Associates (among others).
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|
|
<p> Along with that O'Reilly also publishes a book called something
|
|
like: "Getting Connecting: Establishing a Presence on the Internet"
|
|
(That would be the "Pig" book) by Kevin Dowd). If you're trying
|
|
to set yourself up as an ISP or if your want to have a
|
|
dedicated connection to the net (say for your office) than
|
|
this is probably what you want.
|
|
|
|
<p> Personally I recommend that most small business and private
|
|
people avoid "dedicated" or "permanent/full-time" connections
|
|
to the 'net. It's much less expensive to configure UUCP for
|
|
mail and news -- and look at virtual hosting and/or co-location
|
|
for serving up web pages and other services. This can be
|
|
supplemented with demand dialed PPP (using scripts or diald)
|
|
to provide the web access -- over a modem or via ISDN.
|
|
|
|
<p> One of the big benefits of ISDN is the lower latency. A
|
|
modem connection takes about 30 seconds to 1 minute to
|
|
dial, ring, connect, and negotiate. ISDN can do that in
|
|
about 3 seconds. You'll be much less reluctant to hang
|
|
up and quit hogging your ISP's phone line if you know that
|
|
you can get back in about 3 seconds.
|
|
|
|
<p> In addition to the lower expense running your site as a
|
|
disconnected network relieves you of quite a bit of the
|
|
security concerns associated with a full time net connection.
|
|
Sure -- your PPP link is inherently bi-directional (people
|
|
can connect back to your through it and attempt to exploit
|
|
the same services that they my attack on a fully connected
|
|
site). However you'll be there to notice any additional
|
|
load or any anomalies -- and your whole site is considerably
|
|
less attractive to crackers anyway.
|
|
|
|
<p> (People who connect their Linux systems to the 'net via PPP
|
|
really should take a 1 hr course on securing their hosts.
|
|
Maybe I'll crank out an article on that sometime).
|
|
|
|
Romero,
|
|
|
|
<p> Back to your question. Please try reading up about
|
|
these connections and/or consider hiring a local consultant.
|
|
I don't know anything about the phonesystems in Brazil --
|
|
and I get a little sketchy about ISP's if I get more than
|
|
about 200 miles inland from the Pacific Coast.
|
|
|
|
<p>
|
|
--Jim
|
|
|
|
<p><hr><p>
|
|
<!--================================================================-->
|
|
|
|
<a name="spawn"></a>
|
|
<h3><img align=bottom alt=" " src="../gx/ques.gif">
|
|
Respawning too Fast
|
|
</h3>
|
|
<P> <B>
|
|
From: Igor Markov <a href="mailto:imarkov@math.ucla.edu">imarkov@math.ucla.edu</a>
|
|
My question is about the infamous "Resapawning too fast" message
|
|
from init. This message appears in my /var/log/messages
|
|
every 5 minutes (of course!) for xdm
|
|
I'm just guessing that this is for "The Answer Guy"
|
|
|
|
init: Id "x" respawning too fast: disabled for 5 minutes
|
|
|
|
However, xdm is running (I see it in ps output and I don't have
|
|
problems using it).
|
|
</B> <P>
|
|
</H3> <img align=bottom alt=" " src=" ../gx/ans2.gif">
|
|
You don't show the appropriate lines from your
|
|
your /etc/inittab but they should look something like:
|
|
|
|
<p> # Run xdm in runlevel 5 (and 4 for me)
|
|
x:45:respawn:/usr/bin/X11/xdm -nodaemon
|
|
|
|
<p> (Note: I run xdm in 4 and 5 which unusual -- but
|
|
4 is my custom default -- with 12 VCs, xdm in VC13
|
|
-- accessed by the right alt-key + F1 -- and syslog
|
|
output on VC 15, VC14 is used for stray open commands
|
|
or to redirect pesky output from backgrounded processes).
|
|
|
|
<p> My guess would be that you don't have the -nodaemon
|
|
switch on yours. (Try adding it).
|
|
|
|
<p> If I'm mistaken than the troubleshooting will be
|
|
more involved. Check with the vendor for your
|
|
distribution of Linux and see if they have some
|
|
patches.
|
|
|
|
<p> Red Hat users may want to look at:
|
|
|
|
<a href="http://www.redhat.com/support/docs/errata.html">
|
|
http://www.redhat.com/support/docs/errata.html</a>
|
|
<p> ... to see what's been fixed since your CD was burned.
|
|
|
|
<p> Also you may want to look in your xdm-config file
|
|
(/etc/X11/xdm/xdm-config -- if you're lucky -- otherwise
|
|
it could be in .... /usr/X11R6/....????).
|
|
|
|
<p> The best introduction to xdm I've ever found was in
|
|
_The_Shell_Hacker's_Guide_to_X_and_Motif_ from John
|
|
Wiley & Sons.
|
|
<P> <B>
|
|
<img align=bottom alt=" " src="../gx/ques.gif">
|
|
It seems that init tries to spawn a second xdm.
|
|
I couldn't confirm or reject this hypothesis...
|
|
(egrep xdm /etc/* /etc/*/* did not show anything promising)
|
|
Thank you
|
|
</B> <P>
|
|
</H3> <img align=bottom alt=" " src="../gx/ans2.gif">
|
|
Respawning too fast indicates that the program
|
|
is exiting (pretty much immediately) and that init
|
|
figures that there must be some bad problem. For
|
|
example if getty is respawning it may be that it's
|
|
attempt to grab the serial line is failing (like
|
|
there is no serial driver configured in your kernel
|
|
and you forgot to load the module -- or something like that).
|
|
|
|
<p> If xdm is loading and forking off a daemon (it's default)
|
|
then this will look like an exit/failure to init. The
|
|
-nodaemon will force xdm to run from the console in which
|
|
init started it (not try to "background" itself as it would
|
|
do if you ran it from a command line).
|
|
|
|
<p> The fact that your copy is working suggests this -- but when
|
|
you log out of your xdm session you might have to way upto
|
|
five minutes for init to decide to try xdm again (unless
|
|
your xdm logout configuration is doing the respawning or
|
|
something weird).
|
|
<p>
|
|
--Jim
|
|
|
|
|
|
<p><hr><p>
|
|
<!--================================================================-->
|
|
<a name="map"></a>
|
|
<h3><img align=bottom alt=" " src="../gx/ques.gif">
|
|
Problems with Keyboard Mapping
|
|
</h3>
|
|
<P> <B>
|
|
From: Gilbert R. Payson
|
|
<a
|
|
href="mailto:g.payson@edina.xnc.com">g.payson@edina.xnc.com</a><BR>
|
|
Hello. I have three (okay, four) linux machines in Germany.
|
|
My problem is this: In Xwindows, my keyboard mapping is almost perfect.
|
|
But, there are a few problems:
|
|
</b>
|
|
<p><b> @ doesn't work.
|
|
It brings me to the last edited line (like an up-arrow)
|
|
How can I fix this?
|
|
</b>
|
|
<p><b> thanx! -gil
|
|
</B> <P>
|
|
<img align=bottom alt=" " src=" ../gx/ans2.gif">
|
|
I think you want to look at the xmodmap command.
|
|
You'll also want to look at the following HOW-TO
|
|
documents:
|
|
<ul>
|
|
<li><a href="http://sunsite.unc.edu/LDP/HOWTO/Keyboard-HOWTO.html">
|
|
Keyboard HOWTO</a>
|
|
<li><a href="http://sunsite.unc.edu/LDP/HOWTO/mini/Key-Setup">
|
|
Key Setup mini-HOWTO</a>
|
|
|
|
</ul>
|
|
<p>
|
|
--Jim
|
|
<p><hr><p>
|
|
<!--================================================================-->
|
|
|
|
<a name="modsp"></a>
|
|
<h3><img align=bottom alt=" " src="../gx/ques.gif">
|
|
Modem Speed
|
|
</h3>
|
|
<P> <B>
|
|
From:Scott Atwood<a href="mailto:atwood@cs.stanford.edu">
|
|
atwood@cs.stanford.edu</a><BR>
|
|
I'd like to make a comment regarding a question from "The Answer Guy"
|
|
column in issue 13 of Linux Gazette about combining modems to increase
|
|
speed. This question reflects a common misconception of equating
|
|
bandwidth with speed. Latency is a much more important measure of
|
|
percieved speed, especially in interactive applications, such as
|
|
telnet sessions, and web browsing. Combining modems will increase
|
|
bandwidth, but latency will remain unaffected. For a more complete
|
|
treatment of this subject, see:
|
|
<a
|
|
href="http://rescomp.stanford.edu/~cheshire/rants/Latency.html">http://rescomp.stanford.edu/~cheshire/rants/Latency.html</a><BR>
|
|
an essay by Stuart Cheshire, author of Bolo.
|
|
</B> <P>
|
|
|
|
</H3> <img align=bottom alt=" " src=" ../gx/ans2.gif">
|
|
I finally got around to reading your article. It was
|
|
very interesting.
|
|
|
|
<p> I thought I had warned the reader that doubling his
|
|
bandwidth would only help on large, bulk transfers --
|
|
but perhaps I overlooked it.
|
|
<p>
|
|
--Jim
|
|
|
|
<p><hr><p>
|
|
<!--================================================================-->
|
|
|
|
<a name="duplic"></a>
|
|
<h3><img align=bottom alt=" " src="../gx/ques.gif">
|
|
Duplicating a Linux Installed Hard Disk
|
|
</h3>
|
|
<P> <B>
|
|
I have installed slackware on my PC and I'm completely satisfied. I want
|
|
to duplicate my linux installed hard disk : Can I use my 1st hard disk
|
|
as a source and copy all of its contents to a 2nd blank linux-formated
|
|
hard disk? If I put this 2nd disk into another PC, it will boot Linux
|
|
normally?
|
|
</B> <P>
|
|
<p><img align=bottom alt=" " src=" ../gx/ans2.gif">
|
|
You can just use the 'dd' ("disk dump" or "data dump")
|
|
command on the raw devices. This will work if the two drives
|
|
are identical with no bad sectors.
|
|
|
|
<p> Many years ago I'd have said you were an idiot to even consider
|
|
it. Now I'd recommend against in much milder language.
|
|
|
|
<p> The difference is that modern drives -- IDE and SCSI are
|
|
capable of autotranslation (so the BIOS and often the
|
|
Unix/Linux disk drivers don't need to know the true
|
|
geometry of the disk. Most drives these days also have
|
|
spare sectors on every track -- during a low level format
|
|
spares are mapped into use for any bad sector on a particular
|
|
track. Using this scheme (which is normally completely
|
|
transparent to the host machine -- it's all in the drive's
|
|
electronics) it is rare to see any bad sectors on a drive
|
|
(until all the spares for a given track are used up).
|
|
|
|
<p> So it is technical feasible to do this.
|
|
|
|
<p> However I'd say that you're much safer to spend a little
|
|
more time and "do it right."
|
|
|
|
<p> Use fdisk to partition the new drive (presumably to set its
|
|
partitions to match those on your first drive. You can
|
|
do this without downing the system. I personally prefer to
|
|
follow the advice and reboot after writing a new partition
|
|
table -- but that's probably a force of habit from too
|
|
many years of DOS and OS/2.
|
|
|
|
<p> Then do a<code>mke2fs -c /dev/hdbX</code> (where X is the partition
|
|
number) for each of these new partitions.
|
|
|
|
<p> Then do a:
|
|
<PRE>
|
|
mount /dev/hdbX /mnt/tmp
|
|
find . -mount | cpio -pvum /mnt/tmp
|
|
</PRE>
|
|
<p> ... to each of them.
|
|
|
|
<p> Now your are almost done. The only problem is that
|
|
your lilo boot map (on your existing drive) probably
|
|
doesn't match the lilo configuration on the new one.
|
|
|
|
<p> The most reliable way of dealing with that is to
|
|
take the new drive to the new system -- boot from a
|
|
rescue floppy using the root=/dev/hdaX command
|
|
line parameters (on the lilo prompt line from the
|
|
rescue floppy) and edit the /etc/lilo.conf. Then
|
|
run lilo and reboot.
|
|
|
|
<p> That's all there is to it. That's about seven steps
|
|
(with 3 of them being repeated for each filesystem on
|
|
the drive(s). The amount of time this takes is dwarfed
|
|
by the actual task of opening your case and getting the
|
|
jumpers on the new drive working right (which is far worse
|
|
for IDE than most SCSI in my experience).
|
|
|
|
<p> Why is this better? Well it deals with bad blocks and
|
|
small difference in geometry. It also ensures that the
|
|
new copy is defragmented. Other than that -- it just
|
|
"feels" like a better way.
|
|
|
|
<p>
|
|
--Jim
|
|
|
|
<p><hr><p>
|
|
<!--================================================================-->
|
|
|
|
<a name="fire"></a>
|
|
<h3><img align=bottom alt=" " src="../gx/ques.gif">
|
|
Using the Linux Box as a Firewall
|
|
</h3>
|
|
<P> <B>
|
|
From: Tim Gray <a href="mailto:timgray@lambdanet.com">
|
|
timgray@lambdanet.com</a> <BR>
|
|
Hi, I have a small problem that might affect others out there..
|
|
I am trying to get my linux box to act as a "firewall" of sorts for
|
|
my wife's Windows 95 computer. (I haven't been able to get her to
|
|
switch yet)
|
|
I installed ne2000 compatable boards in each, ran cable, installed
|
|
everything as per
|
|
per linux network administrators guide. The problem I have is
|
|
getting Packets
|
|
destined for internet to go out the modem line when it's not connected.
|
|
I need a way to have linux automatically fire up my dial-up connection when
|
|
it sees that the remote computers want to use it. and possibly kill the
|
|
connection after a period of non use.
|
|
|
|
<P> Thank you. Tim
|
|
</B> <P>
|
|
<img align=bottom alt=" " src=" ../gx/ans2.gif">
|
|
This arrangement is referred to a a "Proxy" server --
|
|
which is only a component of certain firewall architectures.
|
|
|
|
<p> Specifically you appear to be trying to set up a "dial on
|
|
demand Masquerading proxy host." (if I understand you
|
|
correctly).
|
|
|
|
<p> The first tool you need for this is called 'diald' --
|
|
(the 'dial daemon').
|
|
|
|
<p> The most recent version that I know of is at:
|
|
|
|
<p> <a href="ftp://sunsite.unc.edu/pub/Linux/system/network/serial/">
|
|
ftp://sunsite.unc.edu/pub/Linux/system/network/serial/</a>
|
|
<p> ... and is named:
|
|
<PRE>
|
|
diald-0.16.tar.gz
|
|
</PRE>
|
|
<p> I just set this up (literally while this draft was
|
|
loaded in my mailer). It was suprisingly easy.
|
|
|
|
<p> Just edited the make file (just to change the
|
|
LIBDIR, BINDIR, etc directories to point at /usr/local/...)
|
|
did a make and a make install. Then I created a file
|
|
named /etc/diald.conf with just the 'lock' directive in it.
|
|
I did this so I can more readily support multiple diald
|
|
configurations -- as I'll explain presently:
|
|
|
|
<p> I created a /etc/diald/ directory and put in a
|
|
file like:
|
|
<PRE>
|
|
device /dev/modem
|
|
connect "chat -f /etc/ppp/connect"
|
|
speed 38400
|
|
modem
|
|
defaultroute
|
|
crtscts
|
|
redial-timeout 120
|
|
connect-timeout 120
|
|
mode ppp
|
|
dynamic
|
|
local 192.168.1.1
|
|
remote 192.168.1.2
|
|
include /usr/lib/diald/standard.filter
|
|
</PRE>
|
|
<p> Obviously yours will differ in a few spots.
|
|
the -f parameter to your connect line should point
|
|
to whatever chat script you use manually. You might
|
|
change the device line -- although I highly recommend
|
|
that you consistently configure all of your packages to
|
|
use /dev/modem (which is just a symlink to the real
|
|
serical device on my system).
|
|
|
|
<p> I currently have diald, pppd (manual), uucp, kermit,
|
|
minicom, and mgetty all sharing this modem and properly
|
|
using the same lock files throughout.
|
|
|
|
<p> The local and remote addresses are apparently arbitrary --
|
|
I use addresses that are listed in RFC1918 (nee 1597)
|
|
which reserves several sets of addresses which the
|
|
IANA/InterNIC promise not to give out to "real" internet
|
|
sites.
|
|
|
|
<p> Then added the following two lines to my /etc/rc.local:
|
|
<PRE>
|
|
modprobe slip
|
|
/usr/local/sbin/diald -f /etc/diald/rahul
|
|
</PRE>
|
|
<p> (Where the rahul file is the one I've listed above and
|
|
refers to one of my PPP providers).
|
|
|
|
<p> Once you have your system reliably dialing your provider
|
|
on demand -- the next step is to get routing working
|
|
from your wife's system to the internet.
|
|
|
|
<p> I would recommend bringing up the ppp connection manually
|
|
and doing all the routing/masquerading/proxying configuration
|
|
and testing with the line "nailed" up.
|
|
|
|
<p>
|
|
--Jim
|
|
|
|
<!--================================================================-->
|
|
<P> <hr> <P>
|
|
<center><H4>Previous "Answer Guy" Columns</H4></center>
|
|
<P>
|
|
<A HREF="../issue13/answer.html">Answer Guy #1, January 1997</A><BR>
|
|
<A HREF="../issue14/answer.html">Answer Guy #2, February 1997</A><br>
|
|
<A HREF="../issue15/answer.html">Answer Guy #3, March 1997</A>
|
|
<P><HR><P>
|
|
<center><H5>Copyright © 1997, James T. Dennis <BR>
|
|
Published in Issue 16 of the Linux Gazette April 1997</H5></center>
|
|
|
|
<P> <hr> <P>
|
|
<!--================================================================-->
|
|
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